1. Field of the Invention
The invention relates to a device for measuring forces that are generated by unbalance of a rotor.
2. Description of Related Art
A device for measuring forces that are generated by unbalance of a rotor is known, as shown by DE 33 32 978 A1. In such a device, it is known to mount the measuring shaft rotatably in two bearing units arranged at an axial distance from each other and supported via force sensors opposite a hollow bearing housing. This measuring shaft mounting is carried by a stationary frame.
From EP 0 343 265 A1 it is known, in the case of a balancing machine, to mount a backing girderxe2x80x94extending axially relative to the measuring shaftxe2x80x94in a pivotal manner with respect to a stationary frame. Sensors are arranged at an axial distance from each other, between the backing gird and the stationary frame. From DE 33 30 880 A1 it is known to support on a stationary frame a supportxe2x80x94receiving the measuring shaft rotary mountingxe2x80x94via force transmitters arranged at an axial distance from each other
In a device known from EP 0 133 229 A1 used for balancing motor vehicle wheels, the measuring shaft is supported on a stationary frame in a mounting that has a force transmitter. To achieve a dynamic balancing, two mounting planes in which the force transmitters are also arranged are provided for the mounting of the measuring shaft.
From EP 0 058 860 B1 a balancing machine for rotary bodies is known in which the measuring shaft is mounted rotatably on an elastically flexible flat part arranged vertically on the machine bed. For this, the rotary mounting of the measuring shaft is provided at the upper edge of the flat part. Position excursions of the flat part are detected via an arm of sensors running at right angles to the flat part; the sensors"" force initiators run perpendicular to each other. In this connection, one of the sensors records the static portion while the other sensor detects the forces resulting from the dynamic unbalance and causing a twisting of the vertical, elastically flexible flat part around a center line, for example.
Furthermore, from DE-AS 16 98 164 an oscillation-measuring (supercritical) measuring system is known for mounting a rotor on leaf springs positioned diagonally to each other and whose extensions form a virtual intersection in one of the balancing planes of the rotor to be balanced. The two leaf springs positioned diagonally to each other are supported against a base plate via an intermediate plate on vertically standing leaf springs arranged parallel to each other. By means of oscillation transformers the vibrations of the leaf springs resulting from a rotor unbalance are detected and converted into corresponding measuring signals.
From DE-AS 10 27 427 and DE-AS 10 44 531 it is known, in the case of spring bars or plate springs that form oscillatory mountings in balancing machines, to form joints by thinning points.
The force sensors provided in known devices in the mounting planes at the measuring points supply sensor signals that are proportional to the centrifugal forces that result from the rotor unbalance and bring about the reaction forces measured by the sensors. With the conventional standard measuring systems for wheel balancing machines, a floating mounting is typical for the measuring shaft and the rotor clamped onto it. Translation onto the two balancing planes on the rotor for the dynamic balancing of the unbalance takes place based on the force lever law of statics. The forces measured in the two mounting planes by the sensors are thus independent of the respective distance of the rotor from the two sensors. Since these distances are different, a superproportional error in the balancing masses calculated for the respective balancing planes when the sensitivity of one of the two measuring converters is modified due to different influences, e.g. due to temperature, ageing, impact, overload, shaking in transport, humidity influence and the like.
An object of the invention is to produce a device of the type mentioned in the beginning in which, due to the above-mentioned force dynamics a sensitivity modification of a measuring converter only slightly affects the mass balancing to be carried out in the balancing planes, e.g. by balancing weights to be attached.
In accordance with this invention, the above object is attained by a device in which a rigidly designed intermediate frame, on which a measuring shaft is supported in a mounting plane displaying a force sensor, is supported on a stationary frame via a further force sensor. The two force sensors are thus respectively situated in two mounting systems for a force-measuring unbalance detection, with each force sensor assigned to one of the two mounting systems. The two mounting systems are situated between the measuring shaft and the stationary frame, e.g., the balancing machine, on which the unbalance measurement is carried out on a motor vehicle wheel. In this connection, the force sensors may be situated in different mounting planes nevertheless situated in the area of the rigid intermediate frame, or in a common mounting plane.
With the design of the above-mentioned mounting systems, at least one more support is provided for the measuring shaft. The support has the property of a virtual mounting position in a further mounting plane. Two such mounting planes with such virtual mounting positions are provided for. The virtual mounting positions may be situated on both sides of the rotor to be measured. It is also possible, however, to provide for only one additional mounting plane having a virtual mounting position; this plane being situated preferably between the two balancing planes of the rotor or between the planes in which the force sensors are situated and the rotor.
The two force sensors are preferably arranged in a common mounting plane that runs perpendicular to the axis of the measuring shaft. The forces initiated in the force sensors as reaction forces are oriented parallel, particularly coaxially to each other and are situated in the common mounting plane. The force sensors may be situated in the area of the axial extension of the intermediate space in different mounting planes.
In a preferred embodiment, the measuring shaft is supported on the intermediate frame in a first mounting plane displaying a force sensor and in a second mounting plane displaying the virtual support point, and the intermediate fame in the one mounting plane is supported against the stationary frame via the second force sensor and, furthermore, is linked to the stationary frame by means of a parallel guide. The mounting plane displaying the dual support point can be situated between the rotor, particularly a motor vehicle wheel, and the mounting plane that has the two force sensors, or preferably between the two balancing planes of the rotor, particularly a motor vehicle wheel.
The intermediate frame can be supported via a pair of first support levers and joints at the respective ends of the first support levers. The measuring shaft can also be supported via a pair of second support levers and joints at the ends of the second support levers on the intermediate frame. The axes of the respective joints run perpendicular to the plane in which the forces introduced into the force sensors and the axis of the measuring shaft are situated. The pair of first support levers supporting the intermediate frame on the stationary frame can be provided in parallel to each other. For this, the first support levers run parallel to each other. It is also possible, however, to arrange the first support levers at an angle to each other, with the apex of the angle preferably situated in the axis of the measuring shaft or in the vicinity of this measuring shaft axis. The joints of the first support levers define the corners of a trapezoid. With this arrangement, the virtual mounting position situated on the outer side of the rotor is created. The virtual mounting positionxe2x80x94support inside the rotor, particularly between the balancing planesxe2x80x94can also be formed by support levers arranged at an angle to each other and whose joints are supported in the corners of a horizontal trapezoid of the support lever arrangement. The support levers are preferably formed as rigid flat members, e.g., sheet metal parts, cast parts, rolled flat parts and the like which ensure along with the joints that the desired force e.g. running essentially linearly and axially, is introduced into the sensors. The support lever arrangement formed from the flat parts can be designed as a one-piece construction, wherein the flat parts are designed rigid and only the joints situated in between and running essentially linearly are flexible. The joints can be formed by weak points, e.g. constrictions between the individual flexible flat parts. In this way, flexible joint axes are formed between the flexible flat parts. With the corresponding arrangement, parallel or at an angle, the desired virtual mounting positions that are formed in the respective linearly extending mounting axes are then created, as explained above.
The virtual mounting positions are also the measuring points taken into account in the frame calculator of the balancing machine and representing vial measuring points.